表达式求值

#include<bits/stdc++.h>        using namespace std;int cmp(char temp){    switch( temp)    {    case '+':        return 1;    case '-':        return 1;    case '*':        return 2;    case '/':        return 2;    default:        return 0;    }}void fun(string &a, string &b)      // 中缀式转变后缀式{    stack<char>s;    s.push('#');    int i = 0;    while(i<a.length()-1)    {        if(a[i]=='(')        {            s.push(a[i]);            i++;        }        else if(a[i]==')')        {            while(s.top()!='(')            {                b=b+s.top();                b=b+' ';                s.pop();            }            s.pop();            i++;        }        else if( a[i]=='+'||a[i]=='-'||a[i]=='/'||a[i]=='*')        {            while(cmp(s.top())>=cmp(a[i]))            {                b+=s.top();                b+=' ';                s.pop();            }            s.push(a[i]);            i++;        }        else        {            while(a[i]>='0'&&a[i]<='9'||a[i]=='.')            {                b+=a[i];                i++;            }            b+=' ';        }    }    while(s.top()!='#')    {        b+=s.top();        b+=' ';        s.pop();    }    b+='=';}double jisuan(double x,double y,char z){    if(z=='+')        return x+y;    if(z=='-')        return y-x;    if(z=='*')        return x*y;    if(z=='/')        return y/x;}int main(){    int T;    string a,b;    cin>>T;    while(T--)    {        cin>>a;        b="";        fun(a,b);        stack<double>s2;        int len=b.length();        for(int i=0; i<len; i++)        {            if(b[i]=='+'||b[i]=='-'||b[i]=='*'||b[i]=='/')            {                double  x=s2.top();                s2.pop();                double  y=s2.top();                s2.pop();                s2.push(jisuan(x,y,b[i]));            }            if(b[i]>='0'&&b[i]<='9')            {                char c[1005];                int cot=0;                while(b[i]!=' ')                {                    c[cot++]=b[i];                    i++;                }                c[cot]='\0';                double temp=atof(c);                s2.push(temp);            }        }        printf("%.2lf\n",s2.top());        while(!s2.empty())            s2.pop();    }    return 0;}